Create a curve on a mesh
Switch on Proportional Editing. Use sphere falloff.



Select the two middle verts and scale them on the Z axis only. Adjust the radius with the mouse wheel.



Switch off proportional edit, select one row of verts and adjust the thickness.





Did I mention there's another way of doing this? No?

Well, there's another way of doing this:

Create a circle with lots of verts.



Go to side view and rotate the circle a bit with R



Duplicate the circle with  SHIFTD and mirror it with  SZ-1 RETURN.



Move the circle up a bit with G



Deselect with A, use Box Select B to select the right verts and delete them.



Select the two edgelines with  A and bridge them using  SPACE B R I





Did I mention there's yet another way of doing this? No?

Well, there's yet another way of doing this.

Put a Cylinder around your bent faceline. Use an excessive amount of verts, 512 or more. Scale or model it into the desired shape.



Give it a Shrinkwrap Modifier with the settings shown in the picture.



Apply the modifier. Delete the circle.





Just in case you get bored...

There's another way of doing this!

Add a UV Sphere, few segments, lots of rings.



In Top View and Edit Mode, select as shown. Delete.



Select the left half and move to the right. Or select the right half and move to the left. Throw a coin if necessary.



Share and enjoy.